Field of the Invention
The invention relates to a coolable segment of a turbomachinery, in particular a shroud or guide blade plate (guide ring segment) of a combustion turbine. The invention also relates to a combustion turbine having a coolable segment.
An important consideration in the design of a turbomachine, in particular gas turbine engines or steam turbines, is to ensure that various components of the engine are maintained at safe operating temperatures. This is particularly true for elements of a gas turbine like a combustor and a turbine section, which are exposed to the highest operating temperatures in the engine, and which include turbine nozzles or vanes, turbine buckets or rotating blades and shrouds. A turbine nozzle directs hot gas within an annular gas path, to cause the adjacent following bucket row to rotate, producing power. A shroud defines a portion of the gas path radially outward of the rotating bucket row.
In the turbine section of gas turbine engines, high thermal efficiency is dependent upon high turbine entry temperatures. These entry temperatures, in turn, are limited by the heat which the materials forming the turbine nozzles, buckets and shrouds can safely withstand. In cases in which the gas path temperatures are above the material limitations, the gas path surfaces of these components must be cooled to survive. Thus, in addition to improvements in the types of materials and coatings used to fabricate these components, continuous air cooling has been employed to permit the environmental operating temperature of the turbine to exceed the melting point of the materials forming the components without affecting their integrity.
A number of fluid cooling techniques, in particular air cooling techniques, have been used in an attempt to effectively and uniformly cool the components of the turbine section, the combustor and other portions of gas turbine engines.
In European Patent Application EP 1022437A1 to Tiemann at al. an element of a combustion turbine is disclosed which comprises a wall element having an internal coolable area. Between two of those wall elements a gap for allowing compensation of thermal expansion is sealed off by a seal element. The internal coolable area is supplied with cooling air which exits the wall element through a bore opening into the gap whereby the cooling air exiting the bore cools by impingement cooling the wall of the adjacent wall element. After exiting the gap the cooling air flows along an outer surface of the wall element thereby shielding the outer surface from a stream of hot gas flowing in the combustion turbine.
In International publication WO 00/60219A1 to Tiemann et al a turbine-engine with an array of wall elements that can be cooled and method of cooling an array of wall elements is described. This method includes the step of cooling a first element, in particular a portion of a turbine vane by impingement cooling and a further step which includes the using the same cooling fluid for cooling a second component downstream of the first component. For reducing a cooling fluid lost by leakage a cooling passage is formed between the first and the second component for which the cooling fluid flows after cooling the first component. The second component, which is preferably a shroud, is cooled by a cooling fluid in a convection-cooling manner.
Published German patent application DE 19727407 A1 to Krebs refers to a heat shield plate for a combustor of a gas turbine. On the internal wall of the combustor the plates are mounted forming a cavity with the combustors wall. In the wall of the combustor cooling fluid channels directed perpendicular to the walls surface and having openings formed as nozzle into the cavity. These nozzles serve to improve the impingement cooling by a cooling fluid being directed to the plate. The plate itself has a number of diffusion cooling channels leading from the cavity to the outer surface of the plate and being inclined by an angle of about 30 degrees with respect to the outer surface of the plate.
In WO 98/13645 A1 to Gross et al. a closed loop air cooled heat shield component is disclosed. This heat-shield component comprises a cooling-fluid return, a hot-gas wall to be cooled, an inlet duct for conducting a cooling fluid and an outlet duct for returning the cooling fluid. The inlet duct is directed towards the hot-gas wall and widens in a direction of the hot-gas wall.
In WO 99/47874 A1 to Becker at al. a wall segment for a combustion chamber is described which is exposed to a hot combustion gas. The wall segment has a metal support structure and a heat protection element secured thereon. The metal support structure is provided, at least partially covered with a thin heat resistant separating layer. The separating layer is arranged between the metal support structure and the heat protection element. The heat protection element is in addition cooled by cooling gas.
U.S. Pat. No. 5,823,741 to Predmore at al. describes a gas turbine plant, in which components of a nozzle structure are sealed through a seal joint including a sealing member for sealing segmented components of a gas turbine engine. The seal joint is spaced from the gas path to provide more effective cooling. The segments include radial extension flanges spacing the seal joint from the gas path. For the cooling of the segmented components cooling arrangements are shown to provide for open or closed circuit impingement or convection cooling plus film cooling.